1. Field of the Invention
This invention relates to an ink ribbon for thermal transfer used for an image formation method for forming a dye image on a photographic or printing paper by the thermal transfer system.
2. Description of the Prior Art
In order to print out an image photographed by, e.g., an electronic still camera, etc. on a photographic paper in the same manner as in the silver salt system photograph, an attempt has been made to form an image by the thermal transfer system.
In such a thermal transfer system, an ink ribbon is caused to be in contact with a photographic paper on which an image receiving layer consisting of hydrophobic high molecular substance or polymer such as polyester, etc. is formed on a transferred material such as a synthetic paper, etc. to heat the ink ribbon by means of a thermal head, etc. to allow dye included in this ink ribbon to be transferred to the image receiving layer of the photographic paper.
The ink ribbon can be obtained by dissolving dye into an organic solvent together with a binder high molecular substance to coat it on a base. Hitherto, as the dye of this ink ribbon, a disperse dye has been used mainly with a view to ensuring practical sensitivity.
However, in the case where an ink ribbon including such disperse dye is used, it is pointed out that an image formed by the thermal transfer system is remarkably inferior to that of the silver salt photograph in respect of conservative stability, particularly light resistance.
On the other hand, there has been also proposed a method of using, in place of the disperse dye, phthalocyanine anion dye which can obtain excellent light resistance as compared to that of the disperse dye.
However, since phthalocyanine includes a hydrophilic group or radical in the molecule, it exhibits poor or unsatisfactory compatibility with the binder high molecular substance. Accordingly, it is difficult to form a practical image.